High resolution cathode ray tube apparatus



A M A May 17, 1960 N. F. FYLER 2,937,314

HIGH RESOLUTION CATHODE RAY TUBE APPARATUS Original Filed March 5, 1958 6 Sheets-Sheet 1 24 f 27 27 I5 P r m \\'J 6 F I? 32 I! 1 P 17 23 I m 2 T" 33 F, I g N36 25 I I? \\i Y I 33 I 34 \M f a :i 35': 1, F|6.1

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'i INVENTOR.

ATTORNEY May 17, 1960 N. F. FYLER 2,937,314

HIGH RESOLUTION CATHODE RAY TUBE APPARATUS Original Filed March 5, 1958 6 Sheets-Sheet 2 INVENTOR. Norman F/Zler BY attorney May 17, 1960 N. F. FYLER 2,937,314

HIGH RESOLUTION CATHODEI RAY TUBE APPARATUS Original Filed March 5, 1958 6 Sheets-Sheet 3 H5 H9 Sins I20 zll? us 1 i ||7- :1 |2O H9 k I W ll 5b INVENTOR. 'Normon F. Fyler Attorney May 17, 1960 N. F. FYLER HIGH RESOLUTION CATHODE RAY TUBE APPARATUS Original Filed March 5, 1958 6 Sheets-Sheet 4 DISPLACEMENT IN INCHES INVENTOR.

Norman F. Fyler I May 17, 1960 N. F. FYLER HIGH RESOLUTION CATHODE RAY TUBE APPARATUS ori inal Filqd March 5, 1958 6 Sheets-Sheet 5 INVENTOR.

Norman F. Fyl BY c/ h ATTORNEY May 17, 1960 N. F. FYLER 2,937,314

HIGH RESOLUTION CATI-IODE RAY TUBE APPARATUS Original Filed March 5, 1958 6 Sheets-$heet 6 I26 i Z I I! l 1 mo I y FIG.1O

INVENTOR.

Norman F.

F ler I BY//.

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HIGH RESOLUTION (IATHODE RAY TUBE APPARATUS Continuation of application Serial No. 719,229, March if This application December 28, 1959, Serial r1 Claims. c1. 315-17 The present invention relates in general to improved cathode ray tubes and more particularly concerns a high resolution cathode ray tube apparatus capable of producing an exceptionally fine spot of substantially uniform luminous intensity. This is a continuation of my earlier filed application Serial No. 719,229, filed March 5, 1958, entitled High Resolution-Cathode Ray Tube Apparatus, now abandoned.

From the standpoint of commercial television image generation and display, customary cathode ray techniques are readily adaptable to achieve established standards of spot size and resolution. Thus, little difiiculty is experienced in presenting the required 525 line raster on the face of a home television receiving tube or on a flying spot scanner used for video signal generation. Although the emphasis on detail in specialized wideband closedcircuit television systems may require somewhat higher resolution than the 525 line raster, conventional cathode ray tubes may still be employed with little or no modification.

The present invention contemplates and has an important object the provision of a cathode ray tube apparatus offering spot definition and resolution several orders of magnitude finer than heretofore available with tubes designed primarily for television use. Through the application of the inventive concepts herein disclosed, resolution of the order of 1000 lines per inch or more may be achieved on the phosphor target or screen of a cathode ray tube, permitting image reproduction approaching photographic quality, with oscilloscope displays or flying spot scanners having the definition required to read the exceedingly small microfilm frames such as are used for data storage in a Min'icard file system.

Another object of this invention is the provision of suitable structure incorporating an electron optical system for a cathode ray tube capable of providing an extremely fine luminous spot of substantially uniform light intensity.

A further object of this invention is the provision of means for developing a cathode ray tube spot in the form of an exceptionally narrow rectangle, thereby achieving high resolution in one direction and substantially constant average overall light intensity despite any variations in the emissive properties of phosphor particles on the screen, such intensity approaching that achieved in conventional cathode ray picture tubes.

Still another object of the invention is the provision of a cathode ray tube system in accordance with the preceding objects having a high degree in deflection linearity.

Still a further object of the invention is the incorporation of a deflection system for the novel cathode ray tube structure in accordance with the preceding objects capable of displacing the spot to substantially any position on the face of the tube while retaining the desiredhigh resolution without dynamic focusing.

A feature of the invention resides in the provision of an exceptionally narrow slit controllable within precise 2,937,314 Patented May 17, 1960 tolerances and suitably located within the tube for masking an electron beam from a filamentary source.

Another feature of the invention resides in the provision of means for externally controlling the orientation of an internal filamentary electron source relative to a beam masking slit in a completed tube and to maintain such orientation.

Another object of the invention is the provision of an electron gun structure arranged to minimize undesired electric field components within such structure tending to divergethe electron beam emanating from the electron source therein.

Still another object of the invention is the provision of a sensitive. electron 'gun capable of providing marked beam current response to small, high frequency changes in grid potential.

A further object of the invention is the provision of a method for adjusting narrow beam-shaping apertures to precise tolerances.

Still further, it is an object of the subject invention to incorporate the novel gun structure source, masking and orientating means along with conventional components in a cooperative manner within a cathode ray tube type structure to achieve the foregoing objectives.

Broadly speaking, the invention comprises a cathode ray tube envelope having an electron gun which emits a narrow rectangular electron beam of substantially uniform cross-sectional density through an aperture toward a phosphor screen. A substantially uniform axial magnetic focusing field, for example, is etablished in the region traversed by the electron beam between the aperture and screen. The deflection yoke may comprise two pairs of coaxial deflection coils having a cosine distribution of turns in space quadrature about a section of the tube approximately midway between the electron gun aperture and the phosphor screen.

In general, the electron gun includes a filamentary source of electrons adjacent to a control grid and spaced from an accelerating anode formed with a small aperture through which the shaped beam emerges. The disposition of the source, control grid and accelerating anode is such that a substantially axial electric field exists in the region between the filamentary source and the aperture to minimize the beam divergence.

For a specific. application, the filamentary sourceof electrons perpendicularly intersects the gun axis between closely adjacent planar control grid conducting surfaces disposed substantially parallel to both the filamentary source and the gun axis. t

The accelerating anode preferably comprises a known cup-shaped electrode including a conductive surface lying perpendicular to the gun axis formed with an axially symmetric opening. A novel beam-limiting, slit-like aperture is defined by a pair of flat coplanar conductive elements secured to said anode surface and having spaced, closely adjacent, parallel knife edges symmetrically positioned over said opening. A planar electrode is positioned in the region of the edges of the grid surfaces nearest the accelerating anode in a plane perpendicular and parallel to the grid and anode surfaces, respectively. This electrode and the grid conducting surfaces are maintained at substantially the same D.-C. potential. In a preferred form, this planar electrode and grid conducting surfaces are electrically isolated with respect to A.-C. signals. Thus, the desired axial electric field pattern is obtained while the grid-cathode capacity remains relatively low, thereby facilitating the control of beam intensity with high frequency signals.

A novel feature of the invention resides in the provision of means for externally controlling lateral displacement and angular orientation of the filamentary source and control grid surfaces relative to the aperture in the accelfrom the third bimetallic element.

the filamentary source and control grid surfaces are maintained in fixed relationship by an insulating spacer. A pair of bimetallic elements contact one side of the spacer and a third bimetallic element contacts the spacer on the opposite side in the region between the first pair of bimetallic elements. 'An electric heater surrounds each bimetallic element, the current through each heater being individually controllable to regulate the temperature of its own associated bimetallic element. By heating the first pair of bimetallic elements unequally, the spacer may be rotated, while lateral translation may be obtained by heating the first pair of bimetallic elements differently To achieve a visible indication of correct alignment, a phosphor material may be applied to the periphery of the aperture in the accelcrating anode on the side thereof facing the filamentary sources. Uniform illumination about the aperture is indicative of bimetallic heater currents which have properly centered the electron beam on the aperture.

Another feature of the invention resides in the means for retaining the precise position of 'thefilament-grid assembly after the heaters surrounding the bimetallic elements are deenergized, notwithstanding mechanical shocks imparted to the electron gun. This is accomplished by embedding the legs which support the filamentary source in any known material which has a relatively low melting point and is adapted to use in an electron tube. Any one of many well known glasses, of course, have the desired characteristics. The material is heated to its softening point, and the filament-grid assembly then precisely oriented in the manner described above. The material is then permitted to harden about the supporting legs by removing the heat therefrom so that the filament-grid assembly is firmly secured in the desired position.

- Other features, objects and advantages of the invention will become apparent from the following specification ticularly Fig. 1 thereof, a perspective view of a first embodiment of the novel high resolution cathode ray tube apparatus is shown, certain portions having been deleted to disclose interior structure. A cathode ray tube is there shown consisting of an evacuated, generally cylindrical glass envelope 10 having a phosphor screen 11 deposited on an inner, substantially flat, front plate and an electron gun 12 in a neck portion of the envelope 10. The electron gun 12, described in detail hereinafter, emits electrons in the form of an electron beam 13 along the tube axis toward screen 11. Leads from all the electron gun electrodes except the anode electrode are brought out to pins 18 in a conventional tube base 19.

The beam 13 is focused and deflected by magnetic fields produced by a coil assembly 14 which surrounds the tube. The coil assembly 14 includes a solenoidal focusing coil 15 for providing an axial magnetic field H, a vertical deflection coil 15, and a horizontal deflection coil 17, the coils 15, 16 and 17 being mounted upon concentrically arranged individual coil forms of Bakelite or other suitable insulating material as shown. The'vertical deflection coil .16 is disposed within grooves 21 of inner cylindrical form 22 and the region 23 between form 22 and cylindrical form 24 upon which focusing coil 15 is wound. Annular ridges 25 on form 22 separate the latter from focusing coil inner form 24 to provide the region 23.

. the focusing coil 15 may be centered on the envelope 10.

"At the opposite end, focusing coil inner form 24 contacts annular ridge 31 of inner form 22. Focusing coil'15 is enclosed by cylindrical outer focusing coil form 32. Horizontal deflection coil 17 is wound upon the outer cylinwhen read in connection with the accompanying drawing, 7

in which:

Fig. 1 is a perspective drawing of a first embodiment,

of a cathode ray tube apparatus incorporating the invention having portions of the figure cut away to show specific features; a

Fig. 2 is a perspective drawing of a novel-electron gun having'portions removed better to expose the interior structure; v

Fig. 3 is a diagrammatic representation ofthe electric field lines in the electron gun structure shown in Fig. 2;

Fig. 4 illustrates the anode surface of'the electron gun of Fig; 2 as seen from the grid-cathode end thereof;

Fig. 5 illustrates the apparatus ofthe anode'beam limiting aperture shown during one step in the assembly of the accelerating anode of Fig. 2;-

Fig. 6 illustrates a portion'similar tothe one shown in the accelerating anode of Fig. 2 modifiedto have an aperture of precisely controlled dimensions;

Fig. 7 is a broken-away perspective view of an-alternative embodiment of an electron gun accordingto the nvention;

Fig. 8 is a vertical cross-sectional view of a portion of Fig. 7 to show details. of the novel means for retaining Fig. 7; Fig. 9 is a graphical representation of the focusing current for optimum focus of the electron beam as a function of the beam displacement for various deflection yoke positions of a tube made according to. the invert tion and, a

Fig. 10 is a perspective view of a further embodiment of the invention utilizing, anovel electrostatic focusing arrangement. Throughout the drawings and the description thereof, like elements referred to in the different figures are identified by the same reference numeral. r With, reference now to the. drawing, and. more parprecise alignment of components in the gun structure of drical form 33 which is in surface contact with outer focusing coil form 32. 7

Inner and outer forms 22 and 33, respectively may be rotated about and moved along the tube axis to permit proper alignment of the deflection coils as discussed hereinafter. V

Anode '34 of gun 12 is electrically connected to an electrically conducting coating 36, made according to any known processes, as with Aquadag, on the inside of glass wall 26 by the resilient tabs 35, which also serve to position and shock-mount the gun axially within the tube. A high voltage terminal 37, embedded in the envelope 10, contacts the Aquadagv coating 36 and serves to connect accelerating anode 34 to an appropriate external biasing source of potential.- ducting coating also preferably covers the forward interior of the glass wall 26 and the phosphor screen 11, the portion 36 being Aquadag' and the portion '36 being sputtered aluminum, for example. 7

Referring now to Fig.2, there is shown an enlarged perspective view of the novel electron gun with portions cut away to expose elements otherwise not visible.

A cup-shaped base electrode 41, formed with a substantially rectangular, diametrical slot 42, supports a similarly shaped upper electrode 43 by means of a pair of ro'd assemblies, each of which is formed of conductive sections 45 and 46 joined together, but electrically isolated'as by glass beads 47. The conductive rod sections 45 and 46 are preferably Welded in the customary man ner to the cylindrical outer surfaces of electrodes 41 and 43. Electrode 43 is formed with a rectangular slot 44 similar to and preferably aligned with slot 42 in electrode 41. Conductors 48 and 49 couple electrodes 41 and 43 to'difierent pins 18 in tube base 19 (Fig. 1).

Anode 34 (Figs. 1 and 2) is supported axially within the gun by a pair of insulating rods 51, such as glass,

clamped. at opposite ends by rings 52 and 53 attached The electrically conto anode 34' and base electrode 4r;- respeeuvel as through welds, for example.

Two pairs of electrically conductive L-shaped legs 54 and 55 are welded to base electrode 41 over slot 42. Flexible conductive rods '56 and 57 are secured between the upright portions of legs 54 and 55, respectively; pass through insulating bead 61, and support the small, parallel, spaced rectangular conducting plates 62 and 63, preferably being welded thereto. These plates together form the control grid'64 and lie on opposite sides of the thoriated tungsten filament 65.

Filament 65 is supported by flexible conducting members 66 and 67 which pass through insulating bead 61, extend through slot 42 of lower base electrode 41 and are electrically conducted to respective pins 18 in tube base 19 (Fig. 1). One end of filament 65 is welded to tab 71 of member 66. The other end passes freely through a yoke formed by tabs 73 at the upper end of member 67 and is attached to a tension spring 72 which maintains filament 65 under tension at all times. The filament may be fabricated from any electron-emissive material as is known in the art, but in the illustrated embodiment is made of thoriated tungsten wire.

Short rods 74 and 75 extend radially inwardly from glass rods 51, each rod being secured to one of the glass rods 51 as by metal to glass techniques. An L-shaped bimetallic 76 is secured, as by welding, along its base to rod 74 and its upright arm presses against the center of insulating bead 61. A heating element 77 encloses the upright arm of bimetallic element 78, the first end of the heating element 77, being welded directly to the base of the bimetal. A conducting rod 81 is welded to bimetallic element 76, as shown, thus connecting the first end of the heating element 77 to a pin 18 in the tube base 19 (Fig. l). The second end of heating element 77 is welded to a conducting rod 82 which rod, in turn, is connected to another pin 18 in the tube base 19 (Fig. 1), thus completing an electrical circuit through the heating element 77.

Radial rod 75, connected to a separate glass rod 51 in the same manner as rod 74 is connected to glass rod 51, supports a tangentially disposed, short rod 83. L- shaped bimetallic elements 84 and 85 are welded to rod 83 and press against the ends of insulating bead 61 to resist the force applied on the opposite side by bimetallic element 76. Heating elements 86 and 87 surround bimetallic elements 84, 85, respectively'one end of each heater being welded to its corresponding bimetallic element. These ends are electrically connected to a pin 18 in base 19 through rod 83, rod 75 and conducting member 91, as shown. The other ends of heating elements 86 and 87 are each connected to separate pins 18 through conducting members 92 and 93, respectively. It should be noted in passing, however, that the bottom ends of the heating elements 77, 86, 87 may be connected together internally of the electron gun and then connected to a single pin 18.

Anode 34 includes an inverted cup-shaped section 94 formed with spring clips 35, for high voltage connection purposes disclosed in the description of Fig. l. The lower circular anode surface is fo'rmed with a circular opening 95 centered on the axis of the gun. A pair of thin fiatplates 96 and 97 are disposed surface contact with the lowermost surface of anode 34. The closely spaced, confronting edges of plates 96 and 97 are formed with beveled knife edges 101 and 102, respectively, to define a slitlike beam limiting aperture 103 which is parallel to the fiat upper surface of electrode 43, the upper surface of control grid 64 and filament 65. Filament 65 has preferably the same width, but has a greater length than aperture 103.

To complete the gun structure, a getter 104 is fastened to an annular flange 108 extending from the upper edge of the cup-shaped section 94 of anode 34. This getter is flashed in' the customary manner in completing evacation of the tube. Certain features are to be noted with respect to the gun structure described immediately above. First, only the beam from the center portion of filament 65 passes through aperture 103, thereby enhancing the uniformity of the beam electron density. The control grid plates 62 and 63 are spaced very close to filament 65, resulting in an exceptionally high transconductance, yet, the small area of these surfaces minimizes the capacitance between the control grid and the filament. Additionally, by maintaining upper electrode 43 at substantially the same D.-C. potential as control grid '64, the electric field between the anode and control grid in the region traversed by the beam from the filament 65 to the aperture 103 remains substantially'axial and relatively insensitive to signals applied to control grid 64.. As a result of this relative insensitivity, variations of beam divergence due to electric field components orthogonal to the gun axis are virtually eliminated. Since variations in beam divergence are virtually eliminated, secondary defocusing effects attendant on changes in the amplitude of the grid drive signal are small enough to be disregarded in a practical gun. Moreover, since upper electrode 43 is electrically isolated from control grid 64, the interelectrode capacitance between the elements making up the gun is minimized.

The diagram of the electric field distribution in the space between the filament 65 and the anode 34 (Fig. 3) illustrates why beam divergence is virtually eliminated. Before discussing Fig. 3 in detail, it should be noted that the electrode 43, the control grid 6 the filament 65 and the anode 34 are shown in cross-section, the cut-away plane being normal to the knife edges 101, 102 of the anode 34, the longitudinal axis of the filament 65, the plane of the grid plates 62, 63 making up the control grid 64 and the slotted surface of the electrode 43. Further, spacing between the various electrodes has been changed to allow a clearer drawing to be made and the size of the various electrodes has been greatly exaggerated for the same reason. In an actual electron gun made according to the invention, the following dimensions have been used: diameter of the filament 65, .001"; width of slot between grid plates 62, 63, .003"; depth of filament 65 in slot between the grid plates 62, 63, .006"; distance from ends of grid plates 62, 63 to anode 34, .100"; size of aperture 103, .001" x .025". An accelerating potential of 25,000 volts may be applied as desired, by applying potentials to the anode 34 and the filament 65 so that the latter is negative with respect to the former. With electrodes having the foregoing dimensions and an accelerating potential of 25,000 volts, it has been found that relatively low grid drive is required to control the gun. That is, the intensity of the electron beam may be varied from saturation to cutofi with a signal of about five (5) volts amplitude applied to the control grid 64. It should be noted in this respect that the amplitude of the grid signal required for complete control of the electron beam density may be changed by changing the foregoing dimensions, particularly the depth of the filament 65 between the grid plates 62, 63. It is evident from observation of Fig. 3 that, if the filament 65 is placed farther down between the grid plates 62, 63, the grid drive required ot cut off the gun would be greater. It is also evident that the insertion of the filament 65 between the grid plates 62, 63 affords protection to the filament 65 from positive-ion bombardment, since ahnost all such ions are attracted to the control grid 64.

Considering now Fig. 3 in detail, the electric field existing between the electrodes is represented by dotted equipotential lines, it being understood that the illustrated equipotential lines are exemplary only. The trajectories of the electrons (shown in solid lines) emitted from the filament 65 are also exemplary. As is shown,

the equipotential lines are substantially parallel to the oppositely disposed surfaces of the anode 34 and the electrode 43, except for perturbations adjacent the aperture in the anode 34 and the apertures between the control grid 64 and filament 65. Although the perturbations are undesirable in that their presence means thatthe trajectories areafiected to some degree (the paraxial trajectories being curved slightly ina direction orthogonal to the desired direction) the perturbations have been found to have onlya minor'eifect upon dispersion of the name of fAutoflex? or the bimetallic material made by the Metals and Controls Company and known by the trade name Trufiex E-Sjf arranged so as to bend toward the insulating bead 61 when heated. Whatever bimetallic'material is used to make the bimetallic elements, it

I has been found to be advantageous to space the bimetalbeam. It is felt that the reason the perturbations have t such a small efiect is that the accelerating voltage attract ing the electrons toward the anode 34 is so great that' the transit time of the electrons between the filament 65 and the anode 34 is very short, sothe electrons are not in the perturbations for a long enough .timeto have their velocities changed substantially; In any event, the electron beam is clipped by the knife edges 101, 102 so that the electrons having divergent trajectories are removed from the beam; It is understood, ofcourse, that the perturbations adjacent the filament 65 are desirable to effect normal intensity control of the electrons emitted from the filament 65. I

In passing, it should be noted that the knife edges '10 102 are formed by bevelling the plates 96, 97

toward the sides thereof opposite the filament 65. This type of bevel permits very close adjustment of the spacing between the knife edges 101, 102 without danger of blocking the aperture or reducing its eifective width, yet allowing the plates 96, '97 to be made from thick material for mechanical considerations. The plates 96, 97 are preferably fabricated from a soft magnetic material, as, for example, material such as that known in the art by the name m l-metal. When such a material is used, the electromagnetic fields of the focus coil in Fig. l) and the deflection coils (16, 17 in Fig. 1) areshunted away fromthe space between the anode 34 and the filameat 65, leaving only the electrostatic field just described as the etfective operation factor there.

While the foregoing description has been directed particularly toward an electron gun having certain re cited dimensions, and potentials on the various electrodes, it is understood that such dimensions may be changed Without departing from the invention. For example, if it be desired to increase the kinetic energy of the electron beam to brighten the luminescent spot on the viewing screen, the accelerating potential may be increased; .say to 60,000 volts, and the spacing between the filament and anode increased to say .25 to avoid arcing between the anode and the other electrodes.

Since the electron beam in the vicinity of the aperture 103 is very well defined, it is highly. desirable that prolic elements 76, 84, 85 from the insulating bead 61 when the heating elements 77, 86, 87 are not energized in order that normal processing of the tube may be carried on without danger of overstressing either the bimetallic elements 78, 84, 85 or moving the supporting structure of the insulating beadfl.

' Referring to Fig; 4, anode 34 incorporating an aid to electron beam lineup is shown. The edge of the anode aperture 103 on the filament side thereof may be coated with anyknown phosphorescent material 106, such as zinc sulphide, which glows when struck by electrons. Thus, when the beam is centered, the aperture edges are equally illuminated on all sides. If correct centering is not'inn-nediately obtained, the filament-grid assembly is reoriented to direct the beam toward the edgeof lesser illumination as previously described. Alternatively, proper orientation may be determined by measuring the light intensity of the spot on the screen witha photocell '(not shown). The position is optimum when the measured light intensity is a maximum.

Since theanode aperture 103 defines the electron beam cross-section, exceedingly close tolerances must be maintained during assembly. Fig. 5 illustrates one step in the vision be made to ensure centering of the electron beam 7 on the aperture 103 to avoidexcessive clipping at the aperture 103 and'to keep the efficiency of the electron gun as high aspossible. Both objects may be attained by moving thefilament-grid structure as a unit, using the bimetallic elements 76, 84, 85 as shown in Fig. 2. After the tube is completely assembled, exhausted and energized so that the electron beam may be adjusted for optimum coincidence with the aperture 103, the heating elements 77, 86, 87 are energized to heat each associated bimetallic element 76, 84, 85. This heating causes the bimetallic elements 76, 84, 85 to move into contact with the insulating head 61, causing that part, in turn (and the filament 65 and control grid 64 attached thereto) to move. It will be appreciated that any combination of rotational and translational movement in a direction at right angles to a line between bimetallic element 84 and" bimetallic element 85 may be obtained by difierential energization of the heating elements 77', 86, 87. While.

assembly technique, by means of which the narrow dimension of the slit aperture may be closely controlled during fabrication. As shown, flat plates 96 and 97, having knife edges 101 and 102 which define the diametrical edges of the slit, are placed upon the flat underside of anode section 94, Knife edges 101 and 102 are pressed firmly against a shimlll, whose thickness is the precise width of the aperture being formed. The plates 96 and 97 are then spot welded to the flat underside of anode section 94, and the shim 111 is then removed. In the event it is found that the welding operation adversely affects the magnetic properties of the plates 98 and-'97, known annealing processes may be used to restore the plates 96 and 97 to their original state.- I 7 Referring now to Fig. 6, an alternative embodiment showing structure for forming a beam-limiting aperture 103 is shown. As may be noted, the beam-limiting aperture 103, illustrated'in Fig. '6 is square. Plates 96 and 97 are first welded to electrode 94 as described inconnectionwith Fig. 5. A circular wire 112, having a diameter equal to the desiredbeam dimension along the aper ture 103 is then centrally positioned between and perpendicular to the plates 96 and 97 and a second pair of plates 96a and 97a is brought into contact with the wire 112 and welded to the plates 96 and 97. While it is possible that plates 96a and 97a be identical with plates 96 and 97, it is preferred that the plates 96a and 97a be thinned down as shown at 113 in order that secondary emission from the bevelled portions of plates 96a and 97a be minimized and the aperture formed by the plates 96, 97 and 96a, 97a beessentially coplanar.

Referring to Fig. 7, there is illustrated an alternative embodiment of electrongun 12 with the filamentary source and aperture slit crossed to provide a beam 13 of square cross-section; Additional features, which ensure precise alignment over extended periods despite mechanical shocks, are also shown. 7

Since in most aspects the structure of the electron gun in Fig. 7 isrlike that in 2, only the differences will be described, The filament '65 of Fig. 2 is replaced by a ribbonfilament'70, preferably also of thoriated tungsten, with its narrow side facing the anode. This type of filament is characterized by ruggedness and structural rigidity. Since spring 72 maintains the already rigid ribbon filament 70 in tension, sagging is virtually non-existent.

Furthermore, the effects of vibration are absorbed by this type of filament; hence, variations in beam intensity due to filament displacement are minimized.

Aperture 103 is oriented at right angles to the length of filament 70, thereby appreciably restricting the incident electron beam 100 along its long dimension, whereby a beam 13 having a substantially square cross-section is provided.

Rods 50 are welded to upper and base electrodes 43 and 41, respectively. Upper electrode 43 is thereby sup ported and electrically connected to base electrode 41. Since the grid 64 is electrically connected to base electrode 41, grid 64 and upper electrode 43 are at the same potential. It has been found that such connection is quite satisfactory when high frequency modulation of the electron beam is not required.

A small metallic cup 115 is welded to lower electrode 41. Flexible rods 56 and 57, which support head 61 and control grid 64, are welded to the base of cup- 115 and sur rounded by a meltable solid, such as glass 116. A heating element 117, visible through slot 118, is disposed between the wall of cup 115 and glass 116. Heating element 117 is energized through conductors 119 which are connected to respective pins 13 in the tube base 19 (Fig. l). Details of the arrangement of elements in cup 115 are better understood by referring to Fig. 8 which shows a sectional view of the cup 115, the cutting plane being central to the width of slot 118 and across the diameter of cup 115. Flexible rods 56 and 57 are shown welded to the base 115b, the latter benig of U-shaped cross-section. The upwardly extending flange of base 115]; is in surface contact with the outer wall 115a of cup 115 and the inner cylindrical wall 120, the latter wall being formed with a lip extending radially outwardly into contact with outer wall 115a. Heating element 117 occupies the annular chamber bounded radially by inner and outer walls 120 and 115a respectively, at the top by the lip of inner wall 120 and at the bottom by the top edge of base 11512.

Before discussing the advantages obtained from this arrangement, it is to be noted that in Fig. 7, there are only two bimetallic elements 76 and 85, respectively. Element 85 is displaced to the left of its position in Fig. 2 and is fastened directly to rod 75. As a result, both elements 76 and 85 are centrally located on opposite sides of bead 61, thereby controlling only the lateral displacement of the filament-grid'asesmbly in a direction normal to the filament length. Alignment ina direction along thefilament-length is not at all critical in this embodiment, because the cross-sectional length of beam 100 is much greater than the width of aperture 103. It is evident, however, that the three bimetallic elements could also be used here with only design changes required.

' With the arrangement of Figs. 7 and 8, alignment is obtained by energizing heating element 117 to cause the glass 116 to soften sufliciently to permit movement of rods 56 and 57. Heating elements 77 and 87 are appropriately energized to heat bimetallic elements 76 and 85, respectively, until they translate the filament-grid assembly to a position which results in a beam 13 of maximum current density. This position may be determined as described hereinbefore in connection with Figs. 2 and 4. When the assembly is in the optimum position, heating element 117 is deenergized. The glass 116 hardens as it cools, thereby holding the assembly in the optimum position. The heating elements 77 and 87 may then be deenergized. This adjustment is initially made when the tube is first assembled and is not usually required thereafter. However, should unusual circumstances cause the filament-grid assembly to be displaced from its optimum position, it is evident that the adjusting procedure just described 'may' be repeated to move the filament-grid assembly.

While the metallic cup is shown to be of relative ly short length in Fig. 7, so as not to obscure details of the electron gun, the metallic cup 115 may extend almost into contact with the head 61 in order to minimize the possibility of subsequent displacement of the filamentgrid assembly from its optimum position. Cup 115, inner wall and rods 56 and 57 are preferably made of metal having a thermal coefficient of expansion very close to that of the glass contained therein. Many such metals are known in the art, one such being chrome-iron. Although other meltable solids may be employed, glass is preferred as the supporting substance because of the relatively low melting point of many known types. Furthermore, many glasses remain tacky at temperatures just above their softening points so that rods 56 and 57 are supported at all times, although free to move gradually 1, focusing coil 15 overlaps both the phosphor screen 11 and the anode 34. As a result of this overlapping, the focusing field traversed by the beam from the aperture in the anode 34 to the phosphor screen 11 is substantially uniform. Since the focusing field is substantially uniform and the lines of force therein are parallel to a line through the center of the aperture 103 and the center of the phosphor screen 11, all electrons which pass through the aperture 103 follow trajectories formed in accordance with the laws of motion of electrons in a magnetic field in which the lines of force are aligned substantially with the direction of motion of the electrons. That is, all electrons that enter the magnetic field at an angle to the magnetic lines of force therein travel in a helical path and all electrons that enter such a field parallel to the magnetic lines of force therein are unaffected by the magnetic field. The strength of the magnetic field may be adjusted (according to the velocity of the electrons entering therein) so that all the electrons that enter the field (as by passing through the aperture 103) are focused at the same point within the field. It is evident that the strength of the field due to the focusing coil 15 may be adjusted so that all electrons that pass through the aperture 163 in the anode 34 may be focused on the phosphor screen 11. I

It has been found possible to accomplish satisfactory focusing by using a coil, consisting of 14 layers of No. 24 wire with a total of 14,269 turns, forming an 8-ohm coil 22%" long and 7%" in diameter, and passing a current of about 0.2 ampere through the coil. The size of the image on the phosphor screen 11 is then the same size as the aperture 103, when the distance between the aperture 103 and the phosphor screen is approximately 22".

The preferred embodiment of the invention shown in Fig. l, utilizes magnetic deflection by means of a horizontal deflection coil 16 and a vertical deflection coil 17. The field generated by each of the deflection coils is perpendicular to the field generated by the focusing coil 15 in Fig. 1. This means, of course, that the field of the deflection coils '16 and 17 is also perpendicular to the direction in which the electrons are moving toward the phosphorscreen 11. As a result, the field from each of the deflection coils would cause the electrons to travel in a substantially circular path if the fields from each were uniform. However, it has been found preferable to wind each of the deflection coils so that each has a cosine distribution of turns, so that the displacement of the luminescent spot on the phosphor screen 11 is linear with the current applied to each of the deflection coils. Specifically, the horizontal deflection coil 16 having 400 cosine distributed turns of No. 28 wire and exhibiting a deflection sensitivity of 200 milliamperes per inch for a 20,000 volt anode potential has been found to be satisfactory. The vertical deflection coil 17, ofcourse, may be substantially the same as the horizontal deflection coil just described or its sensitivity may be changed as desired. Although conventional bridge-null methods may be used to determine when the horizontal and the vertical deflection coils are aligned so as to be perpendicular to each other, it has been found'desirable'to use the electron bearn itself to determine correct alignment. ,That is, appropriate signals are applied to both the horizontal and vertical deflectioncoils so as to cause the luminescent spot on the phosphor screen 11 to trace a line, inclined, say, at 45 to the horizontal. When such a line is compared to a straight edge, no curvature should be discerni ble'. In the event some curvature is detected, rotation of either, or both, of the deflection coils will result in its elimination.

It is evident that some defocusing must occur when the deflection coils 15, 17 are energized. However, it is a simple matter to vary the strength of the focusing field in accordance with the resultant deflection field to maintain adequate focusing. In a practical tube, the amount of this compensation has been found to be very small in view of the relatively long distance from the aperture 163 to the phosphor screen and the relatively small distance that the beam is deflected on the phosphor screen.

The screen itself has been found to have someeffect on the fineness of the spot which may be obtained. Specifically, it has been found that the thickness of the screen is rather critical. A roughrule. of thumb is that the thickness of the screen should not exceed one-half the size of the luminescent spot to be obtained. When. 35

a thicker screen is used, the intensity of the generated spot is decreased and refraction of light through the phosphor particles making up the screen may occur. Thejlatter problem requires special treatment of the phosphor particles before fabrication of the phosphor screen. First, it has been found highly desirable to use phosphors having initially a very fine particle size, such as the commercially available type P-16 phosphor, which has an average particle size of about four (4) microns. Secondly, such phosphors are agitated in a ball mill for 24 to 36 hours and then used toform the phosphor screen, Conventional methods of screen settling may be followed liven if the foregoing process is used, variations in the lntensity of the spot sometimes occur because the size of the luminescent spot approaches the grain size of the phosphor. 7 However, the structure shown in Fig. 1, wherein the aperture 103 is aligned with the filament 65, minimizes such variations. When the aperture 103 is aligned with the filament 65 a rectangular spot is formed on the phosphor screen 11 and the output of each phosphor particle which is energized is integrated.

Referring now to Fig. 9it may be seen that the position of the deflection coils 16, 17 aflects deflection linearity and focusing. In Fig. 9, the ordinate represents current through the focusing coil 15 required to maintain proper focusing while the abscissa represents deflection of the luminescent spot from the mid-point of the phosphor screen 11, the negative values representing deflection to the left and the positive values representing deflection to the right. The curves marked mid-point, full back, and full forward show the variation in therequired focusing current when the deflection coils are centered (mid-point), moved toward the electron gun (fullback),

It is evident from the curves that substantially lesscorrectron 1s requiredwhen the deflection coils are centered-and,

the deflection angle increases as the deflection angle increases for the following reasons:

(1) The mean length of'the paths of electrons passing through the aperture 103 to the phosphor screen 11 increases as the deflection angle increases, making it necessary for focusing to occur at a greater distance from the aperture as the deflection angle is increased; and (2) the strengthof the resultant magnetic field increases as deflection increases, causing focusing to occur at a lesser distance as the deflection angle increases. The foregoing effects may be minimized by providing a curved phosphor screen so that the mean length of the paths of the electrons passing through the aperture 103 does not change with deflection and, if still necessary, providing a dynamic focusing current.

Referring to Fig. 10, an alternative embodiment of the invention is illustrated. In addition to having all the advantages of fine resolution of the system of Fig. l, the embodiment of Fig. 10 is lighter in weight, which is especially desirable in connection with air-borne systems requiring high resolution. This is achieved by providing an axially disposed focusing electric field through the region within the tube traversed by the beam after leaving the anode aperture. It should be noted, however, if a spot of exceptional resolution is required, the solenoid f0- cusing coil may be retained to provide a supplemental magnetic focusing field; however, fewer turns on such a coil are required than are needed when only magnetic focusing is used to attain the same degree of resolution.

The focusing field-forming structure of Fig. 10 preferably includes axially symmetric bands of a material such as is known in the art by the trade-name of Aquadag" and moved toward the phosphor screen (full forward).

further, that the magnitudeof the required correction then approaches a linear function of the deflection angle. It should be recognized that themagnitude ofthe focusing coil current required for optimum focusing decreases as 36 and 122 and a band of conducting material 125 such as aluminum. A cylindrical layer'120 of semiconductor material, such as ferrous oxide, overlays band 122 and contacts bands 36 and 125 at 121 and 124, respectively. A different potential is applied to the bands 36, 122 and 125 through terminals 37, 123 and 126 respectively. Highest potential is applied to terminal 126, the next highest is applied to terminal 123, while terminal 37 is maintained at the lowest potential of the three.

The potential values are selected so that a substantially uniform potential gradient E is established in the semi.- conducting cylindrical layer 120 and oriented parallel to the tube axis. Since this gradient of potential is the electric field, it follows that a uniform axial electric focusing and accelerating field is obtained. It is to be noted that in the region. extending axially between the gun 12 and the junction 121, a unipotential space exists, ,since the anode 34 and Aquadag coating 36 are at the same potential. On the other side of junction 121, the field gradient changes to a uniform value designated in the drawing as E. Because of circular symmetry, the field in this transition region at edge 121 is axial. Since the beam is substantially on the axis in the region, radial field components further out from the axis can introduce virtually no divergence of the beam.

It is apparent that those skilled in the art may make numerous modifications of and departures from the specific embodiments described herein without departing from the inventive concepts. Consequent y, the invention is to be construed as limited only by the spirit and scope of the appended claims.

What I claim is: t

1. An electron gun structure for developing a rectangular beam of electrons comprising a filamentary source of electrons, means for energizing the filamentary source of electrons, means for establishing an electric field adjacent the filamentary source of electrons consisting of the combination of a pair of control grid plates, the pair of control grid plates being spaced to form therebetween a slot having the filamentary source of electrons centrally dis posed therein and means for applying a first electrical potential to the pair of control grids, an accelerating 13 anode and means for applying a second electrical potential to the accelerating anode, the accelerating anode having a rectangular aperture formed therethrough and aligned substantially parallel to the filamentary source of electrons.

2. An electron gun structure as in claim 1 wherein the width of the slot between the control grid plates is approximately three times the diameter of the filamentary source of electrons, the distance between the end of the slot nearest the accelerating anode is approximately one hundred times the diameter of the filamentary source of electrons and the width of the aperture in the accelerating anode is approximately the same as the diameter of the filamentary source of electrons.

3. An electron gun structure as in claim 1 having, additionally, an auxiliary electrode parallel to the accelerating anode and coplanar with the ends of the control grid plates and means for applying the first electrical potential to the auxiliary electrode.

4. An electron gun structure as in claim 1 having, additionally, adjustable supporting structure for the source of electrons consisting of flexible support means attached to the source of electrons, heat responsive means disposed adjacent the flexible support means for imparting a force to the flexible support means, and means without the envelope and connected therethrough for controlling the heat applied to the heat responsive means.

5. Adjustable supporting structure for elements in an electron gun disposed within an evacuated envelope comprising an insulating bead disposed within the envelope, at least two flexible support members secured through the insulating bead, one end of each of the flexible support members being sealed through the envelope, each element to be adjusted being secured to the other end of a separate one of each of the flexible support members, at least two bimetallic elements secured within the envelope adjacent the insulating bead, independent heating means disposed adjacent each bimetallic element, and independent control means without the envelope cooperating therethrough to control each heating element whereby each bimetallic element is moved into contact with the insulating bead to move the bead and the elements attached thereto.

6. Adjustable supporting structure as in claim 5 having, additionally, a glass sleeve disposed about the flexible support members between the insulating bead and the envelope, independent heating means surrounding the glass sleeve and cooperating with independent control means without the envelope whereby the heating means surrounding the glass sleeve may be energized to soften the glass sleeve during the period the insulating bead is being moved.

7. In an electron gun for generating a high resolution electron beam, apparatus comprising, a flexibly supported source of electrons, means for forming an electron beam from electrons emitted from the source, an electrode spaced from the source having a beam-limiting aperture formed therein, phosphor material disposed about the edge of the aperture, heat responsive means for imparting a force to the source to change the direction of the electron beam, and means for controlling the heat applied to the heat responsive means to direct the electron beam at the aperture whereby all portions of the phosphor material are equally illuminated by the electron beam when the electron beam is directed at the aperture.

8. A cathode ray tube system comprising an elongated evacuated glass envelope having in combination a phosphor screen disposed on the inner side of one end thereof, an electron gun disposed at the opposite end of the envelope, the electron gun consising of a filamentary source of electrons, a pair of control grid plates forming a narrow slot with the filamentary source of electrons disposed therein and an anode spaced from the control grid plates toward the phosphor screen, the anode consisting of a plate fabricated from a soft magnetic material and having a rectangular aperture formed therethrough, means for separately energizing the filamentary source of electrons, the control grid and the anode to cause a rectangular beam of electrons to pass through the aperture, and an electromagnetic focusing coil helically wound about the envelope and extending from the anode to the phosphor screen, and means for energizing the electromagnetic focusing coil whereby a uniform axial magnetic field is provided within the envelope between the anode and the phosphor screen.

9. A cathode ray tube system as in claim 8 having, additionally, flexible support means for the filamentary source of electrons and the control grid, heat responsive means for moving the flexible support means and means operating through the envelope to control the heat ap pIied to the heat responsive means to move the filamentary source of electrons and the control grid to center the electron beam on the aperture. p

10. A cathode ray tube comprising an evacuated glass envelope, a phosphor screen disposed on the inner sur-' face of one end of the envelope and an electron gun disposed on the other end of the envelope, the envelope between the phosphor screen and the electron gun being substantially cylindrical, focusing means consisting of a plurality of annular bands of electrically conductive material sequentially disposed on the inner surface of the cylindrical portion of the envelope, means for applying electric potential through the envelope to the annular bands to form a series of electron lenses between each annular band, and a continuous layer of semiconducting material over-laying the annular bands and the remaining surface of the cylindrical portion of the envelope to re duce the electric potential gradient between each annular band.

11. In a high resolution tube, a strip-like source of electrons having an emissive surface, means for energizing said source, a control electrode having a leading edge and symmetrically disposed relative to said source to establish a focusing field for bringing electrons emitted from said source into substantial parallelism into an electron beam of prescribed cross-section, said emissive surface being disposed rearwardly of said leading edge of said control electrode, and a further electrode arranged along the path of said beam, said further electrode having an aperture formed therein corresponding to the beam cross-section and disposed in substantial axial alignment with and parallel to said emissive surface.

12. In a high resolution tube according to claim 11, means mounting said strip-like source for adjustment in relation to said aperture in said further electrode, and means controlled externally of said tube for adjusting said strip-like source.

13. In a high resolution tube, a strip-like source of electrons having an emissive surface, means for energizing said source, a control electrode having a leading edge and symmetrically disposed relative to said source into substantial parallelism into a rectangular electron beam, said emissive surface being disposed rearwardly of said leading edge of said control electrode, means for applying a focusing potential to said control electrode, a further electrode arranged along the path of said beam, said further electrode having a rectangular beam-forming aperture therein disposed in substantial axial alignment with and parallel to said emissive surface, and means for applying a potential to said further electrode which is positive relative to the potential on said control electrode.

14. In a high resolution tube, a support, a strip-like source of electrons having an emissive surface, means mounting said strip-like source for adjustment relative to said support, means for energizing said source, a control electrode having a leading edge and symmetrically disposed relative to said source to establish a focusing field for bringing electrons emitted from said source into substantial parallelism in an electron beam of a prescribed cross-section, said emissive surface being disposed rear- 15 w rdly at said ing c serof aid c n r e q r de means forapplying a focusing potential to' said control electrode, and accelerating electrode arranged along the path of the beam, said accelerating electrode having an aperture formed therein susbtantially of said cross-section and disposed in substantial axial alignment with and parallel to said emissive surface, means for applying an accelcrating potential to said accelerating electrode which is positive with respect to the focusing potential, electrically responsive positioning means for moving saidjstrip-like source to an adjusted position, and means external to i said tube for controlling said positioning means.

'15. In a high resolution tube, a support, a strip-like source of le r ns in n i i c surface, eans mounting said strip-like source for adjustment relative to d pp m an en r z ng sa sou c a cont o ,trode which is positive with respect tothe focusing potential, electrically responsive positioning means for moving said strip-like source to an adjusted position, and means external to said tube for controlling said positioning means. a

16. In a high resolution tube, a support, a source of electrons having an emissive surface, means mounting said source for adjustment relative to said, support, means for energizing said source, a control electrode symmetri- 16 cally disposed relative to saidsource to establish a focusing field for bringing electrons emitted from said source into substantial parallelism in an electron beam, means for applying a focusing potential to said control electrode, an'lac cele'rating electrode arranged along the path ofthe beam, said accelerating electrode having a beamforming aperture therein disposed in substantial axial alignment with and parallel to said emissive surface, means for applying an accelerating potential to said accelerating electrode which is positive with respect to the focusing potential, electrically responsive positioning means for moving said source to an adjusted position, and means external to said tube for controlling said positioning means. 7

17. In an electron gun assembly, a source of electrons for producing an electron beam, means including at least one electrode having a beam-forming aperture therein for controlling said electron beam, means mounting said source of electrons for adjustment in relation to said beam-forming aperture of" said one electrode, electricallyresponsive positioning means for moving said source of electrons to an adjusted position, and means external to said tube for controlling said positioning means.

References Cited, in the file of this patent UNITED PATENTS 1,870,975 Ulrey Aug. 9, 1932 2,111,942 Schlesinger Mar. 22, 1938 2,151,992 Schwartz Mar. 28, 1939 2,194,547 Haines Mar. 26, 19.40 2,480,462 Garbe Aug. 20, 1949 2,483,457 Feldt Oct. 4, 1949 2,516,704 Kohl July 25, 1950 2,565,533' Szegho Aug. 28, 1951 2,810,091 Harsh Oct. 15, 1957 Patent No. 2 937314 UNITED STATES PATENT OFFICE Norman E; Fyler 'It is herebi certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5, line 30, and column 8 line ll for "78" each occurrence, read 76 same column 8 line 41, for "98" read 96 column 9 line 31, for "benig" column 14,, line 56 after "source" insert to establish a focusing field for bringing electrons emitted from said source e Signed and sealed this 15th day of November 1960.

(SEAL) Attest:

KARL H. AXLINE Attesting Ofiicer ROBERT C. WATSON Commissioner of Patents read being P'atent No, 2,937,314 May 17,, 1960 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Norman E; Fyler It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5, line 3O and column 8, line 11, for "78" each occurrence, read 76 -3 same column 8 line 41, for "98" read 96 column 9 line 31 for "benig" read being column 14 line 56, after "source" insert to establish a focusing field for bringing electrons emitted from said source Signed and sealed this 15th day of November 1960.

(SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents 

